The invention relates to a semiconductor laser chip and also a method for fabricating a semiconductor laser chip.
In the field of optical telecommunications, in particular, it is necessary to guide a laser beam emitted by a semiconductor laser into an optical fibre and to transmit said laser beam through the optical fibre from a transmitter, the semiconductor laser, to a receiver, for example a telecommunications switching element or else a further communications element, generally an optical receiver.
Coupling the emitted light power of an edge emitting semiconductor laser into an optical fibre is made considerably more difficult by the lack of near-field spot matching between the semiconductor laser and a customary optical fibre.
The spot diameter of a customary semiconductor laser is approximately 1 xcexcm to 2 xcexcm for the fundamental mode, preferably 1.5 xcexcm transversely and 2 xcexcm to 3 xcexcm laterally.
In an optical fibre, the spot diameter is determined by its core diameter and lies in a region of 6 xcexcm.
Without additional measures, the lack of near-field spot matching explained above leads to semiconductor laser chip/optical fibre coupling efficiencies of less than 10% to 20% in particular in the region of the wavelength range of 1.3 xcexcm to 1.5 xcexcm which is important for optical message transmission.
In order to improve the semiconductor laser chip/optical fibre coupling efficiency it is known to provide a coupling-in optical arrangement having a single-lens or multi-lens system, by means of which the laser beam emitted by the edge emitting semiconductor laser chip is focused by means of the coupling-in optical arrangement as beam shaper and is coupled into the optical fibre in a corresponding form matched in respect of spot diameter.
The coupling-in optical arrangement is usually arranged between the semiconductor laser chip and the optical fibre that is to be coupled to the semiconductor laser chip.
According to the prior art, however, the entire system of semiconductor laser chip/coupling-in optical arrangement/optical fibre is realized as a hybrid arrangement, for which reason a considerable disadvantage of this system can be seen in the requisite high-precision and thus complex adjustment of the coupling-in optical arrangement or of the lenses present in the coupling-in optical arrangement relative to the semiconductor laser chip.
Consequently, the invention is based on the problem of specifying a semiconductor laser chip and also a method for fabricating a semiconductor laser chip with which laser light is coupled into an optical fibre in a simplified and thus cost-effective manner, with coupling efficiencies comparable to those of the known system.
The problem is solved by means of the semiconductor laser chip and also by means of the method for fabricating a semiconductor laser chip having the features in accordance with the independent patent claims.
A semiconductor laser chip has a semiconductor laser element and a beam shaper integrated into the semiconductor laser chip. The beam shaper serves for shaping a laser beam emitted by the semiconductor laser element and is arranged in a manner integrated in the semiconductor laser chip in the exit direction of the laser beam emitted by the semiconductor laser element in such a way that the laser beam emitted by the semiconductor laser element is guided through the beam shaper and its beam shape is altered in accordance with the configuration of the beam shaper and the laser beam altered by the beam shaper can be fed to an optical fibre, for example. The beam shaper preferably has a predetermined concentration profile of oxidized aluminium.
In a method for fabricating a semiconductor laser chip, a semiconductor laser element is formed and a beam shaper is formed in the exit direction of a laser beam emitted by the semiconductor laser element, in such a way that the emitted laser beam is guided through the beam shaper.
The beam shaper is formed as follows:
a beam shaper region is formed in the exit direction of a laser beam emitted by the semiconductor laser element, the beam shaper region containing aluminium,
a desired aluminium concentration profile is formed in the beam shaper region,
a selective oxidation of the beam shaper region is carried out, in such a way that the beam shaper is formed depending on the aluminium concentration profile.
The invention can clearly be seen in the fact that both the semiconductor laser element and the beam shaper, which essentially corresponds to a coupling-in optical arrangement, are integrated together in a semiconductor laser chip.
The invention has significant advantages over the prior art.
In particular, the semiconductor laser chip according to the invention is compact, simple to fabricate and, on account of the integral embodiment, highly insusceptible to disturbances and robust.
Furthermore, complex adjustment of the coupling-in optical arrangement as in the case of the hybrid arrangement in accordance with the prior art is no longer necessary.
Preferred developments of the invention emerge from the dependent claims.
The beam shaper can be monolithically integrated into the semiconductor laser chip.
Furthermore, the beam shaper can have aluminium-containing material, preferably a material combination of at least one of the following material systems:
indium gallium aluminium antimonide (InGaAlSb),
gallium aluminium arsenide antimonide, (GaAlAsSb), or
indium aluminium arsenide antimonide (InAlAsSb).
Since aluminium oxide, in particular, has a lower refractive index than the semiconductor material usually used for the semiconductor laser element, the desired beam shaper functionality can be realized very exactly by oxidation of the aluminium-containing material by means of selective wet oxidation or dry oxidation of a beam shaping region, thereby forming the beam shaper.
Between the semiconductor laser element and the beam shaper it is possible to provide a trench and/or a groove, which separate the semiconductor laser element and the beam shaper from one another in such a way that an air gap is formed in the exit direction of the semiconductor element, at the laser beam exit edge thereof, between the laser beam exit edge and the laser-end entry region of the beam shaper, which air gap may, for example, be filled with a predetermined dielectric.
The air gap and/or the trench clearly form a front side mirror which can advantageously be used in particular when an FP laser (Fabry-Perot laser) is used.
However, even without the air gap, for example a configuration of the semiconductor laser element as a DFB laser (Distributed Feed Back laser) forms a highly efficient semiconductor laser that is insusceptible to disturbances.
The beam shaper can be configured in such a way that the light beam emitted by the semiconductor laser element is brought to a desired form, for example focused, in accordance with the optical laws.
Thus, the beam shaper can also be configured as a concave or convex lens in order to realize the corresponding beam shaper function.
The trench or the spacing between the laser beam emission edge of the semiconductor laser element and the laser-beam-end surface of the beam shaper preferably lies in a region of at most 15 xcexcm.
The beam shaper can be formed for example by forming a beam shaper region in the exit direction of a laser beam emitted by the semiconductor laser element, said region containing aluminium or aluminium-containing material.
A desired aluminium concentration profile is formed in the beam shaper region and a selective oxidation of the beam shaper region is subsequently carried out in such a manner that the beam shaper is configured in the desired shape depending on the aluminium concentration profile.
This procedure, in particular, is distinguished by its simplicity and the small number of process steps required for fabricating the semiconductor laser chip together with the coupling-in optical arrangement, i.e. the beam shaper.
A further advantage of the invention is to be seen in the fact that a high semiconductor laser chip/optical fibre coupling efficiency is coupled in when the laser beam which is emitted by the semiconductor laser element and is guided through the beam shaper is coupled into an optical fibre.